1. Field of the Invention
This invention relates to optical waveguide devices and in particular passive optical waveguide devices.
2. Art Background
Passive optical waveguide devices are utilized in a variety of ways. For example, it is often desirable to transfer lightwave information from one optical fiber to another. Significantly more complicated couplers for transfer of optical information are also required. Passive waveguide devices (often denominated optical couplers) are required to allow transfer of information from all fibers in a collection of fibers to all fibers in a second collection. An optical coupler is exemplified in FIG. 1 where information coming from a fiber in collection 5 is transferred to all the fibers of collection 7.
A coupler-based application receiving a great deal of attention involves optical backplanes. For complex electronic systems, such as electronic telecommunication switches and computers, the interconnection of electronic circuit boards is complex, costly and space-consuming. Indeed, capacities are presently being limited by electromagnetic interference associated with dense electrical interconnections at high information transfer rates, e.g. rates typically above 1 Mbit/sec. One method of easing this complication and increasing capacity is the optical transference of information between circuit boards. A structure utilized for this purpose is typically called an optical backplane. An exemplary backplane is shown in FIG. 2 and includes inputs, 9 on circuit boards 17, outputs, 10, and a coupler within structure 14.
Practically, the advantage of increased capacity is concomitantly diminished by increased cost. The couplers in an optical backplane generally significantly affect the cost. Therefore, nominal coupler cost is essential. Various optical couplers have been proposed. However, their production yields are quite low and their cost high. For example, in one fabrication technique, a portion of the cladding on a plurality of glass optical fibers is removed by etching and the bared core portions are twisted together. This twisted mass is fused under tension to produce a monolithic waveguiding structure between two optical fiber collections. Not only is the cost of this structure quite high, but also the optical properties are variable and are not entirely desirable, e.g. a non-uniform distribution of optical modes occurs in the output collection.
Some molding techniques have been employed in an attempt to produce less complex, more easily fabricated optical interconnections. For example as described by T. Yoshizawa and T. Kawata in Plastics in Telecommunication IV (Rubber and Plastics Institute, 11 Hobart Pl., London U.K.) 1986, pages 11/1 to 11/7, a transparent silicone mold defining a cylindrical void is produced. Optical fiber collections are inserted in each end of the mold. An ultraviolet (UV) radiation-curable core resin is introduced into the mold and solidified by UV irradiation through the transparent mold. The mold is then removed and a lower refractive index UV-curable cladding resin is placed over the hardened resin and solidified to complete the coupler. The fabrication procedure for this coupler is still relatively complex and has only been demonstrated for large diameter fibers in small collections. Therefore, a low cost passive optical waveguiding device such as an optical coupler having versatility and desirable optical properties is not presently available.